Clinical and necropsy observations are described in 61 patients with a healed trasmural myocardial infarction, 33 with and 28 without clinical histories of acute myocardial infarction. No significant differences occurred between the two groups of patients in mean age, sex, or frequency of angina pectoris, chronic congestive heart failure, systemic hypertension, sudden coronary death or fatal acute myocardial infarction. compared to the patients with clinically recognized acute myocardial infarction, the patients with clinically unrecognized (silent) infarction had a significantly (p less than .05) higher frequency of diabetes mellitus (43% - vs-15%), death from noncardiac causes (39% -vs-9%), posterior (inferior) wall infarcts (82% - vs - 55%), and smaller infarcts (mean size 7% - vs-17% of left ventricular wall). The patients with and without clinically-recognized infarcts had similar numbers of the four major coronary arteries severely (76-100% in cross-sectional area) narrowed (mean 2.8 - vs - 2.9/4.0 per patient), insignificant differences in frequencies of severe narrowing of the left main coronary artery (18% - vs - 29%), similar overall percents of 5-mm segments of the 4 major coronary arteries severely narrowed (43-vs-55%), left anterior descending (39%-vs-33%) and left circumflex (41%-vs-41%) coronary arteries.